A hologram is a photographic recording of a light field, rather than of an image formed by a lens, and it is used to display a fully three-dimensional image of the holographed subject.
Current pseudo-holographic technology utilizes an optical illusion known as Pepper's Ghost that exhibits a hologram image reflected through the 2D screen as if the hologram image is floating. Thus, this technology may be referred to as a floating hologram.
Light travels at different speeds in different mediums. Thus, when light travels from one medium to another, light may be refracted on a surface of another medium. Visible light which can be seen by the human eye has the wavelength in the range of from about 400 nm to about 700 nm. When light passes through a prism, the light travels from air to the prism to air. In this case, the light is refracted twice and the angle of incidence of the light is refracted at a certain angle.
A prism can split white light into a spectrum, and the wavelengths of the white light may be refracted differently from each other. A short wavelength (violet) of the spectrum is refracted the most and a long wavelength (red) of the spectrum is refracted the least. Light in nature is white light and includes all of analog frequency components. However, a display represents light in nature by a combination of the three primary colors: red (R), green (G), and blue (B).
Referring to FIG. 1, an image output on a display is represented by a combination of red, green, and blue. Each pixel 103 of the image output on the display includes a red sub-pixel 105, a green sub-pixel 107, and a blue sub-pixel 109.
Since the sub-pixels 105, 107, and 109 have different wavelengths from each other, when a light ray 111 of each pixel 103 passes through a prism 100, the light ray 111 of each pixel 103 is split into a light ray 113 of the red sub-pixel 105, a light ray 115 of the green sub-pixel 107, and a light ray 117 of the blue sub-pixel 109 due to a difference in refractive index among the wavelengths of the respective sub-pixels 105, 107, and 109.
When an observer sees the image through the prism 100, chromatic aberration in which a floating hologram image corresponding to the image output on the display looks blurry may occur due to a difference in refractive index among the light ray 113 of the red sub-pixel 105, the light ray 115 of the green sub-pixel 107, and the light ray 117 of the blue sub-pixel 109.
Japanese Patent No. 3685417 discloses a configuration in which a first prism sheet and a second prism sheet are arranged in almost parallel to each other to minimize dispersion of light passing through the first prism sheet and the second prism sheet.